1. Field of the Invention
The present invention relates to a moving member for a surface acoustic wave actuator and a surface acoustic wave actuator using the same.
2. Description of Prior Art
Surface acoustic wave actuators have potential for use as small linear actuators due to their advantages of high speed and high thrust driving capabilities with a small size. FIG. 1 illustrates a basic configuration of a conventional surface acoustic wave actuator. In the illustrated surface acoustic wave actuator, a moving member (or slider) 4 with an elastic force supply source 11 for providing a pressing force is mounted on a stator 1 with IDTs (Interdigital transducers) 2 and 3 deposited on both sides thereof. In connection with performance of the surface acoustic wave actuator it is shown in a report appearing on page 275 of Proceedings in the 21st Symposium on Ultrasonic Electronics that a drive force of approximately 8N is obtained by pressing a slider against a surface acoustic wave device with a force of 80N, the slider made of silicon has a large umber of projections of pillar form on Its contact surface. It is also shown therein that the drive force is improved by increasing the contact rate (contact area per slider surface area) and pressing force.
On the other hand, in the configuration of the surface acoustic wave actuator shown in the above report, energy of the surface acoustic wave excited by the IDTs is used only partially for driving the slider, while the other greater part thereof is consumed by a absorber, so that the energy efficiency is greatly deteriorated. For solving this problem there has been proposed such an energy efficiency improving method as is disclosed in JP-A Nos. 10-296186 and 11-146665. In such a power-saving type surface acoustic wave actuator, energy of a surface acoustic wave which has passed through a portion of contact with a slider without being used for driving the slider, is circulated and is combined with energy of a newly excited surface acoustic wave to improve the energy efficiency.
For improving the energy efficiency by using the method disclosed in the above unexamined publications or another method involving circulation of a surface acoustic wave energy, it is necessary that the phase of the circulated surface acoustic wave and that of the excited surface acoustic wave be made coincident with each other. If there is a phase shift, the energy of the circulated surface acoustic wave and that of the excited surface acoustic wave offset each other partially, making it no longer possible to improve the energy efficiency. However, if a slider having a high contact rates is pushed against a stator for the purpose of increasing the drive force and improving the drive efficiency, there occurs a change in phase of the surface acoustic wave which has passed the portion of contact with the slider, depending on the magnitude of the pressing force. FIG. 2 is an example of an experimental result in the prior art, showing how the phase of a surface acoustic wave which has passed the portion of contact with the slider varies according to the magnitude of the pressing force.
Such a phase change makes it impossible to improve the energy efficiency, resulting in that the drive efficiency as an actuator can no longer be improved. Also in case of setting the pressing force to a force of one-cycle phase shift it is necessary to make the change of phase uniform throughout the whole of the slider or take an appropriate measure against a change in the state of contact between ON and OFF conditions, thus also involving a difficulty in the improvement of drive efficiency.
The present invention has been accomplished in view of the above-mentioned points and it is an object of the invention to provide a moving member like a slider for a surface acoustic wave actuator which undergoes little change of phase under the action of a pressing force and which can improve the drive efficiency of the surface acoustic wave actuator, as well as a surface acoustic wave actuator using the moving member.
For achieving the above-mentioned object, in a first aspect of the present invention there is provided a moving member for a surface acoustic wave actuator, which is pushed against a stationary member having a surface acoustic wave exciting means and to which a drive force is imparted through a frictional force by a surface acoustic wave propagated on the stationary member, characterized in that projection-arranged portions and gap portions are formed in parallel with the surface acoustic wave propagating direction on a contact surface of the moving member for contact with the stationary member in such a manner that the ratio of the width of each of the projection-arranged portions to that of each of the gap portions is in the range of between 1:4 and 1:10.
According to this configuration, a change of phase is caused by a change in propagation speed which results from contact of projections with the stationary member, so projection-arranged portions and gap portions are formed in parallel with the surface acoustic wave propagating direction on the contact surface of the moving member for contact with the stationary member, that is, gap portions not influenced by the contact of projections are formed, allowing a surface acoustic wave to be propagated therethrough at a constant propagation speed, whereby the influence of a phase change of the surface acoustic wave having passed the projection-arranged portions can be suppressed.
As a result, it becomes possible to increase the pressing force for pushing the moving member against the stationary member and hence possible to increase the drive force and improve the drive efficiency of the surface acoustic wave actuator.
Preferably, the ratio of the width of each of the projection-arranged portions to that of each of the gap portions is set to a value in the range of between 1:4 and 1:10. This is because both improvement of energy efficiency and improvement of drive force can be attained and it is possible to improve the drive efficiency. If the ratio is lower than 1:4, the phase change becomes too large to improve the energy efficiency, and if the ratio is higher than 1:10, the contact rates becomes too low to improve the drive force.
With the moving member for a surface acoustic wave actuator according to the present invention, there occurs little change of phase caused by the pressing force and it is possible to improve the drive efficiency of the surface acoustic wave actuator. According to the moving member for a surface acoustic wave actuator in the first aspect of the present invention which is pushed against a stationary member having a surface acoustic wave exciting means and to which a drive force is imparted through a frictional force by a surface acoustic wave propagated on the stationary member, projection-arranged portions and gap portions are formed in parallel with the surface acoustic wave propagating direction on a contact surface of the moving member for contact with the stationary member in such a manner the ratio of the width of each of the projection-arranged portions to that of each of the gap portions is in the range of between 1:4 and 1:10. With this configuration, a change in phase of the surface acoustic wave having passed the contact portion is suppressed by the surface acoustic wave propagated through the gap portions, thus making it possible to increase the force for pushing the moving member against the stationary member and thereby increase the drive force, whereby there is obtained a surface acoustic wave actuator of a high drive efficiency.
In a second aspect of the present invention there is provided, in combination with the above first aspect, a moving member for a surface acoustic wave actuator wherein all the gap portions are equal in width. According to this configuration it is possible to obtain a phase change suppressing effect which is uniform throughout the whole of the moving member.
In a third aspect of the present invention there is provided, in combination with the above first aspect, a moving member for a surface acoustic wave actuator wherein two or more projections are formed in each of the projection-arranged portions. According to this configuration it is possible to improve the phase change suppressing effect because a change of phase is suppressed by the surface acoustic wave propagated through the gap portions each formed between adjacent projection portions.
In a fourth aspect of the present invention there is provided, in combination with the above third aspect, a moving member for a surface acoustic wave actuator wherein the projections formed in each of the projection-arranged portions are arranged at an equal interval. According to this configuration the phase change suppressing effect can be further improved because the phase change suppression by the surface acoustic wave propagated through the gap portions is effected at a constant interval.
In a fifth aspect of the present invention there is provided, in combination with the above first aspect, a moving member for a surface acoustic wave actuator wherein all of the projections formed in the projection-arranged portions are the same in shape. According to this configuration it is possible to unify the influence of phase change.
In a sixth aspect of the present invention there is provided, in combination with the first aspect, a moving member for a surface acoustic wave actuator wherein each of the projections has a contact area of not larger than 400 xcexcm2. According to this configuration it is possible to diminish the change of phase caused by the projections and hence possible to further improve the phase change suppressing effect by the surface acoustic wave propagated through the gap portions.
In a seventh aspect of the present invention there is provided, in combination with the above first aspect, a moving member for a surface acoustic wave actuator wherein a contact ratio in the whole of the moving member is in the range of between 0.01 and 0.25. According to this configuration it is possible to suppress the phase change while ensuring a contact area required for improving the drive force and so there is obtained a surface acoustic wave actuator of a high drive efficiency.
In an eighth aspect of the present invention there is provided a surface acoustic wave actuator using a moving member which is pushed against a stationary member having a surface acoustic wave exciting means and to which a drive force is imparted through a frictional force by a surface acoustic wave propagated on the stationary member, the moving member having projection-arranged portions and gap portions, the projection portions and the gap portions being formed in parallel with the surface acoustic wave propagating direction on a contact surface of the moving member for contact with the stationary member in such a manner that the ratio of the width of each of the projection-arranged portions to that of each of the gap portions is in the range of between 1:4 and 1:10. According to this configuration, even if the pressing force for pushing the moving member against the stationary member is made large, a change in phase of the surface acoustic wave having passed the contact portion is suppressed and so there is obtained a surface acoustic wave actuator of a high drive efficiency.
In a ninth aspect of the present invention there is provided a magnetic disk unit using a surface acoustic wave actuator as a head driving actuator, the surface acoustic wave actuator using a moving member which is pushed against a stationary member having a surface acoustic wave exciting means and to which a drive force is imparted through a frictional force by a surface acoustic wave propagated on the stationary member, the moving member having projection-arranged portions and gap portions, the projection-arranged portions and the gap portions being formed in parallel with the surface acoustic wave propagating direction on a contact surface of the moving member for contact with the stationary member in such a manner that the ratio of the width of each of the projection-arranged portions to that of each of the gap portions is in the range of between 1:4 and 1:10. By using a surface acoustic wave motor according to the present invention there is obtained a magnetic disk unit superior in access performance.
In a tenth aspect of the present invention there is provided an optical disk unit using a surface acoustic wave actuator as a head driving actuator, the surface acoustic wave actuator using a moving member which is pushed against a stationary member having a surface acoustic wave exciting means and to which a drive force is imparted through a frictional force by a surface acoustic wave propagated on the stationary member, the moving member having projection-arranged portions and gap portions, the projection-arranged portions and the gap portions being formed in parallel with the surface acoustic wave propagating direction on a contact surface of the moving member for contact with the stationary member in such a manner that the ratio of the width of each of the projection-arranged portions to that of each of the gap portions is in the range of between 1:4 and 1:10. By using a surface acoustic wave motor according to the present invention there is obtained an optical disk unit superior in access performance.
Thus, the moving member for a power-saving type surface acoustic wave actuator according to the present invention has projection-arranged portions and gap portions formed on its surface for contact with the stationary member in parallel with the surface acoustic wave propagating direction in such a manner that the ratio of the width each of the projection-arranged portions to that of each of the gap portions is in the range of between 1:4 and 1:10. According to this configuration, a change in phase of the surface acoustic wave having passed the contact portion can be suppressed by the surface acoustic wave propagated through the gap portions, so it becomes possible to increase the pressing force for pushing the moving member against the stationary member and hence possible to increase the drive force, whereby there is obtained an excellent effect that the improvement in drive efficiency of the surface acoustic wave actuator can be attained.
Accordingly, it is a first object of the present invention to provide a moving member for a surface acoustic wave actuator which undergoes little change in phase under the action of an external pressing force and which therefore can improve the drive efficiency of the actuator.
It is a second object of the present invention to provide a surface acoustic wave actuator using a moving member which undergoes little change in phase under the action of an external pressing force and which therefore can improve the drive efficiency of the actuator.
These objects and advantages of the present invention will become more apparent from the following embodiment of the invention taken in connection with the accompanying drawings.